This chapter outlines the physical logictics of installing a wireless network into a building. Concerns regarding the architecture and layout of the building are addressed, so that you can plan appropriately.

Often when a decision is made to install a WLAN, the decision makers do not
realize that WLAN installation sites vary widely. Those who decide to move to
wireless networks understand their environment and assume that most other WLAN
systems and sites are much the same as theirs, and therefore the WLAN
installation should be similar (and easy). Even in something as similar as a
chain of retail stores, minor variations such as stock and shelving arrangements
can cause coverage to vary. In reality, unless the two sites are built from the
same architectural plans and populated with users and contents in a similar way,
the two seemingly similar sites can be as different as night and day. Before a
survey or installation is scheduled, each site needs to be evaluated
separately.

This chapter addresses site-specific issues relevant to WLAN survey and
installation tasks. This chapter examines topics such as site layouts, facility
contents, building and construc-tions variations, different environmental
conditions at the site, and other site-specific requirements. This chapter also
discusses the need for accurate floor plans, building and construction
specifics, an inventory of building contents, and an awareness of customer
issues related to specific installation limitations.

Recommended Facility Documentation

Any engineer surveying and installing a WLAN system needs facility
documentation, the collection of which should be part of the initial design
stage. Facility documentation ena-bles the engineers defining the WLAN, or
trying to survey and install it, to identify areas of concern, areas of
coverage, user densities, and even types of antennas to consider, before ever
walking onto the site. After the survey has been completed, the facility
documentation becomes a critical part of the overall documentation and should be
kept current as to any changes and maintained with the rest of the network
documentation for future reference. The facility documentation should include
(but is not to limited to) the following:

Site map (or floor plans)

Building construction details

Building contents inventory

User-area and user-density information

Problem-area (for WLAN) information

Site Map

Before beginning any site survey, obtain a good site map or floor plan of the
site. In some cases, the site map might not really be a floor plan, but more of
a site layout, including building layout and contents as well any outdoor areas
that will be covered.

This site layout document will become part of the final survey and network
documentation. As such, having a soft copy of this document is very helpful so
that it can be copied and distributed as necessary to the survey engineers,
installation team, and network support staff. Extra copies of the site map
should be available to make notes on during the actual survey and installation
steps, as well as during any presurvey discussions.

Prior to the survey, you can use the site map document to define desired
coverage areas; identify where coverage is not needed; and define user locations
and densities, problems areas, network closets, cable runs, and plenum areas.
Basically, this document becomes the physical schematic of the wireless network
(see Figure 8-1).

Building Construction

Building construction can vary widely from site to site. Materials and
construction techniques in San Francisco differ significantly from those used in
New York City, London, or Cairo. Differences in building construction, even
though sites might look similar, can cause RF to react in completely different
ways. Figure 8-2 shows
examples of various building materials.

A multifloor building might use precast, reinforced concrete for flooring.
Although this type of construction might create some attenuation problems for
RF, the effect on RF penetration is significantly less than it would be with a
floor of poured concrete over a steel pan. Although some RF may get through in
this latter example, the steel pan provides a very good RF shield between floors
(see Figure 8-3).

Walls can be similarly deceiving. In most industrial buildings, it is common
to use steel studs with drywall or plasterboard over them. The drywall and
plasterboard cause only a slight attenuation of RF signals, and the placement of
the steel studs has little effect at all. Other walls might be concrete block,
with or without steel reinforcement, which cause only limited attenuation of RF.
However, precast concrete, typically using steel reinforcement, is a different
story. The amount of steel used for reinforcement inside the concrete will cause
the RF attenuation to vary from one building to another.

Although drywall and plaster usually minimally affect RF, the material behind
the wall can pose problems. Consider a real example from a health-care facility.
The RF energy was having a hard time getting into several offices. Further
questioning of maintenance personnel at the facility and reviewing some older
building documents revealed that this area had been remodeled recently. Before
the area was used as offices, it was the radiology department. The x-ray room
had been turned into offices. And, as typical with x-ray rooms, the walls were
shielded to prevent x-ray energy from leaking out of the room. The walls were
not removed, just covered over; therefore, the RF could not get into the
offices.

In some buildings, the walls might be made from a form of reinforced wire
mesh, with a plaster-type material spread across it (often called
stucco). The mesh can work much like an RF screen, causing a severe level
of signal loss or RF attenuation.

Steel outside walls, or steel walls separating parts of a building, can
detrimentally affect RF coverage (because the wall might not just restrict RF
penetration, it might also create a large number of multipath signals). This is
common in industrial facilities, where a building has undergone one or more
additions. What was once the outside wall might now be a partition between the
old and new sections of the building, causing both multipath signals and an RF
shield between building sections.

Be sure to research this information before or during the survey and document
your findings on the site map.

Building Contents

One often-overlooked area of concern is the building contents. Those with
minimal WLAN and RF experience sometimes underestimate the effect that building
contents can have on a WLAN.

Figure 8-4 shows
several examples of problems that can occur in a typical office environment.
Areas such as file rooms and storage rooms are often filled with steel cabinets,
creating a very large RF shield for RF entering that room, or even passing
through it to other areas of the facility. Although most would assume an area
filled with cubicles should have minimal effect on RF, it might in fact create a
challenge for RF coverage. The number of cubical partitions, the amount of steel
in the partitions and desks, and the size and make-up of the bookshelves can
affect RF range.

Another area that is very difficult to cover is a library or documentation
area. Shelves full of books are shelves full of paper, and most paper has a high
level of attenuation to WLAN frequencies. It is very common for WLANs to use
directional antennas, focusing the RF energy down the aisles of the books.
(See Figure 8-5.)
Because of similar shelving, ware-houses and even some retail stores also use
directional antennas in this way.

Kitchens and break-rooms usually contain microwave ovens. Microwaves are also
found around many health-care and industrial facilities for purposes other than
heating food. Although microwaves pose no problems for 5-GHz WLANs, they can be
problematic for 2.4-GHz WLANs. The typical microwave oven uses the same
frequencies as a 2.4-GHz WLAN. (This is because 2.4 GHz is the resonant
frequency of water, and when 2.4-GHz energy strikes water molecules, it is
absorbs the energy and causes the molecules to vibrate, creating friction and
heat.) Locating a 2.4-GHz access point (AP) close to a microwave can
cause undue interference and result in poor RF communications. Take care to keep
these APs (and clients when possible) at least 10 feet away from any standard
microwave oven. It is therefore recommended to note the location of any such
devices on the site map. Also be aware that industrial microwave ovens sometimes
have a much higher power than those found in the home or office, possibly
creating even more interference. Testing should in-clude RF coverage
verification while any microwaves in the local vicinity are in full operation.

In one case, a health-care facility was having trouble with one particular AP
that was dropping all associations intermittently. Close inspection of the
facility turned up a microwave oven in an area that was not part of the
RF-covered area, but was located in a lab adjacent to the AP-covered area. The
problem was that the oven was located on the other side of the wall (made from
drywall) from the AP, with a total of about 5 feet (and two pieces of drywall)
separation. This is why it is important to understand the entire site, including
areas where coverage may not be needed.
Figure 8-6 shows a
site map with potential problem areas labeled.

Locations such as emergency rooms and cardiac care in hospitals use sensitive
equipment such as electrocardiographs (EKGs) and other monitoring
systems. Although these devices are not generally a problem with WLANs, take
care to locate the radio gear near the devices and to verify that the RF in the
area does not cause any interference. One common problem occurs with older
plotters and printers. The RF energy can cause slight variations in the print
and plotter driver mechanisms, resulting in "glitches" in the patient
printouts.

As discussed in Chapter 6, "Preparing for a Site Survey," all
cordless and wireless devices should be inventoried. Phones, speaker, cameras,
cordless mice, cordless keyboards, baby monitors, and virtually anything that
might be RF related should be noted.

In a warehouse, retail environment, or even an office building, a change of
contents can greatly affect the coverage of an AP. Inventory levels often change
in a warehouse or retail facility. At certain times of the year (such as early
November, when stock levels rise for the holiday shopping season), stock levels
in some facilities may reach beyond 100 percent, with material placed in any
possible free space, such as directly in front of the AP that provides coverage
to the area. This poses a real problem for the survey engineer who is trying to
survey when the stock level might be at a low level corresponding to the season.
(Many installations occur during the off-season, when facilities are not running
at peak capacity.)

Defined User Areas and Densities

The topic of user density has been brought up many times in this book. As
stressed prev-iously, defining user areas and densities is a crucial part of the
design and must be on the minds of design engineers and survey engineers at all
times. The overall performance of the WLAN system depends on proper user
density.

There have been surveys based on nothing but user density. At one very large
software company, the buildings were all built in a very similar manner, and
with identical internal design and contents. All cubicles were identical, all
office construction was identical, and the number of users in a given area was
very similar.

For this customer, it was decided that the applications used by
nonengineering employees would permit between 20 and 25 users per AP. This
provided adequate performance for normal operational network load. The
engineers, however, required a bit more perform-ance, and the user density was
lowered to between 10 and 15 users per AP.

Based on information such as this, some of the design can be done up front.
You can use the site map to determine how large the cell coverage needs to be.
For example, a survey determined that a single AP set to default power levels,
with dipole antennas, could provide coverage for many more users (based on their
seating locations) than the design calls for. In this particular case, the
desired coverage turned out to be a small circle on the site map, and was about
the size of a coffee cup. From this point, it was a matter of defining how many
"coffee cups" were needed
(see Figure 8-7). The
engineers then selected the power setting to provide the proper coverage for the
user density in the appropriate areas. Finally, testing was completed to prove
the guesstimations of the coffee cup survey.

If voice is to be used over the WLAN, it is vital to the design to understand
the capacity of the AP versus the number of calls that can be carried by one AP
at any given time. Typically, a standard 802.11b AP supports only between six
and eight calls with the standard com-pression used in 802.11 voice over
IP (VoIP) phones. As compression techniques improve, or as the wireless
802.11 VoIP phones move to support 802.11g or 802.11a, the number of calls per
AP will increase.